Homework 13 (not graded; only some example ques!ons for the material from the last week or so of class)

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Walter Clement Shelton
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1 Homework 13 (not graded; only some example ques!ons for the material from the last week or so of class)! This is a preview of the draft version of the quiz Started: Apr 28 at 9:27am Quiz Instruc!ons Question 1 If the Hubble Constant is 150 km/s/mpc, then the age of the Universe is 6.5 billion years. Hubble originally measured the Hubble Constant to be 500 km/s/mpc, over 3 times larger. What effect would Hubble's original measurement have on the calculated age of the Universe? It's a trick question...hubble's Law relates galaxy distances and brightnesses, not ages The calculated age would be only about 2 billion years, younger than the age of our Sun The calculated age would be roughly the same The calculated age would be about 20 billion years, much larger than the true value Question 2 Because of the general expansion of the Universe, all distant galaxies appear to be moving away from the Earth, with speeds that increase with distance from our Galaxy. What would be seen by an observer in one of these distant galaxies, called "Galaxy A"?

2 The same thing we see: all galaxies would appear to be moving away from Galaxy A, with galaxies that are farther away from Galaxy A moving faster All galaxies would appear to be moving towards Galaxy A, with galaxies that are farther away from Galaxy A moving faster All galaxies would appear to be moving away from Galaxy A, with galaxies that are closer to Galaxy A moving faster All galaxies on one side of the sky would appear to be moving towards Galaxy A and all galaxies on the other side of the sky would appear to be moving away from Galaxy A Question 3 In our Universe, we can consider four different regimes of space in which distances between objects might be changing as a result of the general expansion of the Universe: (1) distances between different parts of the Earth, (2) distances between planets in our Solar System, (3) distances between stars in the Milky Way Galaxy, and (4) distances between clusters of galaxies. In which of these regimes are the distances changing because of the expansion of the Universe? 4 and 3 4, 3, 2, and 1 4, 3, and 2 4 only Question 4 At the present time, how many exoplanets have been directly confirmed to exist by observing an exoplanet transiting in front of its host star? None

3 One Thousands Millions Question 5 The idea that life might exist in Europa's oceans was boosted by the possible discovery of microbes on the far side of the Moon in a lake deep beneath Antarctica on extraterrestrial meteoroids in the frozen atmosphere above the Earth's poles Question 6 In the Drake equation for estimating the number of advanced civilizations in our Galaxy, why might the factor for the rate at which stars form exclude stars with masses greater than about 1.5 times that of the Sun? Such stars have much shorter lifetimes than it took for intelligent life to develop on the Earth and so should probably not be considered Such stars never develop nuclear fusion in their interiors and hence can never heat any planet sufficiently to sustain life Such stars would never develop nuclear processes that could produce the heavy elements (e.g., iron) needed for planet formation Such stars are prone to repeated and violent supernova explosions throughout their lives, which would destroy any developing life-forms

4 Question 7 Light from the most distant quasar currently known in the Universe took billion light-years to reach the Earth. If it takes at least 100 million years for a black hole to grow to supermassive proportions then this quasar tells us with certainty that Hubble's constant must be smaller than or about equal to 75 km/s/mpc most of the gas in the Universe had already been eaten by black holes or locked up in stars 12.9 billion years ago most of the mergers between galaxies in the Universe had already occurred 12.9 billion years ago this quasar cannot be driven by a supermassive black hole Question 8 What is surprising about the exoplanets that have so far been discovered? Many exoplanets have strong oxygen lines in their spectra, a possible indication of life on these planets Many rocky exoplanets rotate much faster than similarly sized terrestrial planets in our Solar System Many exoplanets are giant planets like Jupiter, orbiting at distances characteristic of terrestrial planets Many exoplanets are terrestrial planets orbiting at distances characteristic of giant planets like Jupiter

5 Question 9 Probably the most difficult factor to estimate in the Drake Equation is R*, the rate at which stars form in our Galaxy f, the fraction of stars that have planets p n, the number of planets per star system that are Earthlike (suitable for life) e L, the lifetime of a technologically advanced civilization Question 10 The cosmological redshift is the stretching of the wavelengths of photons as they travel through expanding space Doppler shift of photons that are emitted by galaxies that are moving away from us loss of energy of photons as they climb away from the powerful gravity of black holes reddening of photons as they pass through clouds of intergalactic and interstellar dust Not saved Submit Quiz

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